Calibration and stabilization of an active noise cancelation system

Abstract

A fixture for calibrating an active noise canceling (ANC) earphone, the calibration fixture including an ear model and an acoustic path. The ear model is configured to support an ANC earphone and includes an ear canal extending from an outer end of the ear canal to an inner end of the ear canal. The acoustic path is external to the ear canal and extends from, at a first end of the acoustic path, the inner end of the ear canal of the ear model to an opposite, second end of the acoustic path. The acoustic path is configured to transmit a mechanical sound wave received from the inner end of the ear canal to a region external to the ear model and adjacent the outer end of the ear canal.

The invention claimed is: 
     
       1. A calibration fixture for noise canceling earphone, the calibration fixture comprising:
 an ear model configured to support the noise-canceling earphone, the ear model including an ear canal extending from an outer end of the ear canal to an inner end of the ear canal; and 
 an acoustic path external to the ear canal and extending from, at a first end of the acoustic path, the inner end of the ear canal of the ear model to an opposite, second end of the acoustic path, the acoustic path being configured to transmit a mechanical sound wave received from the inner end of the ear canal to a region external to the ear model and adjacent the outer end of the ear canal. 
 
     
     
       2. The calibration fixture of  claim 1  further comprising a damping partition between the inner end of the ear canal and the first end of the acoustic path, the damping partition configured to reduce an amplitude of the mechanical sound wave received at the acoustic path from the inner end of the ear canal. 
     
     
       3. The calibration fixture of  claim 2  in which the damping partition is configured to reduce an acoustic effect of an air volume of the acoustic path. 
     
     
       4. The calibration fixture of  claim 2  in which the damping partition comprises resistive cloth. 
     
     
       5. The calibration fixture of  claim 2  in which the damping partition comprises foam. 
     
     
       6. The calibration fixture of  claim 1  in which the ear canal is configured to anatomically resemble a human ear canal, and in which the ear model further includes a concha configured to anatomically resemble a human ear concha and a pinna configured to anatomically resemble a human ear pinna. 
     
     
       7. The calibration fixture of  claim 1  further comprising an ANC earphone secured to the ear model, the noise-canceling earphone having a speaker and a feedforward microphone, the speaker of the noise-canceling earphone being substantially adjacent the outer end of the ear canal of the ear model, in which the feedforward microphone is in the region external to the ear model. 
     
     
       8. The calibration fixture of  claim 7  in which the acoustic path is further configured to transmit the mechanical sound wave received from the inner end of the ear canal to the feedforward microphone of the noise-canceling earphone. 
     
     
       9. The calibration fixture of  claim 1  in which the ear canal has a volume between 1 milliliter and 2 milliliters. 
     
     
       10. A fixture for a noise canceling earphone during calibration, the fixture comprising:
 an ear model including an ear canal extending from an outer end of the ear canal to an inner end of the ear canal; and 
 an acoustic path external to the ear canal and extending from, at a first end of the acoustic path, the inner end of the ear canal of the ear model to an opposite, second end of the acoustic path, the acoustic path being configured to transmit a mechanical sound wave received from the inner end of the ear canal to a region external to the ear model. 
 
     
     
       11. The fixture of  claim 10  further comprising a partition between the inner end of the ear canal and the first end of the acoustic path, the partition configured to alter an amplitude of the mechanical sound wave received at the acoustic path from the inner end of the ear canal. 
     
     
       12. The fixture of  claim 11  in which the partition is configured to match an impedance of the ear canal to a known impedance of a typical human ear canal. 
     
     
       13. The fixture of  claim 11  in which the partition comprises resistive cloth. 
     
     
       14. The fixture of  claim 11  in which the partition comprises foam. 
     
     
       15. The fixture of  claim 10  in which the ear canal is configured to anatomically resemble a human ear canal, and in which the ear model further includes a concha configured to anatomically resemble a human ear concha and a pinna configured to anatomically resemble a human ear pinna. 
     
     
       16. The fixture of  claim 10  further comprising a noise canceling earphone supported by the ear model. 
     
     
       17. The fixture of  claim 16  in which the noise canceling earphone has a speaker and a feedforward microphone, the speaker of the noise canceling earphone being substantially adjacent the outer end of the ear canal of the ear model, and the feedforward microphone being in the region external to the ear model. 
     
     
       18. The fixture of  claim 17  in which the acoustic path is further configured to transmit the mechanical sound wave received from the inner end of the ear canal to the feedforward microphone of the noise canceling earphone. 
     
     
       19. The fixture of  claim 10  in which the ear canal has a volume between 1 milliliter and 2 milliliters. 
     
     
       20. The fixture of  claim 10  in which the acoustic path is further configured to transmit the mechanical sound wave received from the inner end of the ear canal to a region adjacent the outer end of the ear canal.